This invention relates to a cathode ray tube convergence system for a television receiver wherein a cathode ray tube has a plurality of electron beam sources formed to effect underconvergence within and convergence of electron beams exterior to the cathode ray tube and a toroid-wound deflection yoke affixed to the cathode ray tube with horizontal and vertical deflection windings for effecting deflection of the electron beams with the horizontal deflection windings providing converged electron beams at the outer ends of a horizontal axis of the cathode ray tube screen.
In prior known television receivers it has been a common practice to construct a cathode ray tube such that the electron beams are statically converged at the center of the viewing screen of the cathode ray tube. To achieve convergence at the outer ends of the horizontal and vertical axes as well as at the corners of the viewing screen, a deflection yoke and an electro-magnetic convergence means associated with the cathode ray tube are energized by potentials having a proper waveform. Thereupon, the statically converged electron beams available at the center of the viewing screen are not only deflected both horizontally and vertically but also dynamically converged at the extremities of the deflection.
Athough the above-mentioned electron beam convergence system has been and still is employed in numerous forms of television receivers, it has been found that it leaves something to be desired. Specifically, it has been found that such systems require large amounts of driving power in order to effect the desired corrections. Moreover, alteration in convergence at one side of the viewing screen usually affects the convergence on the opposite side of the viewing screen. Thus, a multitude of adjustments are necessary in order to achieve the desired uniformity of electron beam convergence.
One known effort to improve the above-described conditions is set forth in U.S. Pat. No. 3,849,679 issued to Marvin E. Miller on Nov. 19, 1974. Therein, a triad of electron beams is statically converged at the beginning and ending of the horizontal and vertical scan lines. Dynamic convergence apparatus is employed for effecting convergence of the electron beams at the center of the viewing screen. Thus, a plurality of magnets are employed to alter the electron beams derived from the cathodes of a cathode ray tube in a manner such that the beams are statically converged at the ends or periphery of the cathode ray tube screen. Moreover, dynamic correction potentials are applied to a dynamic converger apparatus to effect the desired center correction.
In another known effort to improve convergence in a cathode ray tube system, the cathode ray tube employs a plurality of electron beam sources aligned in a single plane. These electron beam sources are either aligned in a manner such that the electron beams are directed in parallel toward the viewing screen or in a divergent manner by a pair of outer guns directed in a divergent manner. A series of quadrupole windings are included on a deflection yoke associated with the cathode ray tube and these quadrupole windings serve to effect convergence of the electron beams throughout the viewing screen. Moreover, a corrector is also employed to insure the desired convergence of the electron beam.
Although the above-described techniques appear to have provided improvements over prior well-known deflection systems, it is believed that each leaves something to be desired. Specifically, the use of magnetic fields to effect electron beam distortion and convergence of these beams at the outer ends of the cathode ray tube requires increased electron beam influence and increased power to overcome the distortions due to the magnetic fields. Also, an electron beam deflection system wherein the generated electron beams are either parallel or divergent requires considerable power consumption to effect both static and dynamic convergence of those electron beams. Further, employing a relatively large amount of energy in the quadrupole windings to effect convergence tends to produce an undesired poor resolution condition at the corners of the viewing screen.